A common trend in the maintenance of office equipment, particularly copiers and printers, is to organize the machine on a modular basis, wherein certain distinct subsystems of a machine are bundled together into modules which can be readily removed from machines and replaced with new modules of the same type. A modular design facilitates a great flexibility in the business relationship with the customer. By providing subsystems in discrete modules, visits from a service representative can be made very short, since all the representative has to do is remove and replace a defective module. Actual repair of the module takes place away at the service provider's premises. Further, some customers may wish to have the ability to buy modules “off the shelf,” such as from an office supply store. Indeed, it is possible that a customer may lease the machine and wish to buy a succession of modules as needed. Further, the use of modules, particularly for supply units such as toner bottles, is conducive to recycling activities.
U.S. Pat. No. 4,961,088 discloses the basic concept of using an electronically-readable memory permanently associated with a replaceable module which can be installed in a digital printer. The embodiment disclosed in this patent enables a printer to check an identification number of the module, to make sure the module is authorized to be installed in the machine, and also enables a count of prints made with the module to be retained in the memory associated with the module.